Fillers are added to plastics for enhancement of various structural, processing, and application properties. Anti-block products are commonly used in plastic films to lessen the adhesion or blocking of the plastic film surface. This can be achieved by slightly roughening the film surface through surface treatment with wax/polymers or by adding anti-block filler products into the plastic films. Commercial anti-block filler products include synthetic silica, natural silica (such as diatomaceous earth), and other mineral products such as talc, calcium carbonate, and nepheline syenite. These additives are intended to produce microscopic roughness on the surface of the film to minimize the flat contact between adjacent layers, in particular, to prevent individual layers from sticking to one another or “blocking.”
Although synthetic silica has good anti-block performance and optical properties, its high cost can limit its applications in plastic films. Diatomaceous earth is an effective anti-block agent with a more moderate cost. The anti-block performance of other mineral products such as talc, calcium carbonate, and nepheline syenite are typically not as effective compared to diatomaceous earth.
Mineral fillers have been added to thermoplastic and thermoset materials to improve their properties, including tensile strength, heat distortion temperature, and modulus. Besides providing improved properties, fillers also reduce costs since the filled thermoplastics are sold in even larger volumes than neat thermoplastics.
Thermoplastic materials are those which typically soften under the action of heat and harden again to their original characteristics on cooling. By conventional definition, thermoplastics are typically straight and branched linear chain organic polymers with a molecular bond. Examples of well-known thermoplastics include products of acrylonitrile butadiene styrene (ABS), styrene acrylonitrile (SAN), acrylate styrene acrylonitrile (ASA), and methacrylate butadiene styrene (MBS). Also included are polymers of formaldehyde, known as “acetals”; polymers of methyl methacrylate, known as “acrylic plastics”; polymers of monomeric styrene, known as “polystyrenes”; polymers of fluorinated monomers, known as “fluorocarbons”; polymers of amide chains, known as “nylons”; polymers of paraffins and olefins, known as “polyethylenes,” “polypropylenes,” and “polyolefins”; polymers composed of repeating bisphenol and carbonate groups, known as “polycarbonates”; polymers of terephthalates, known as “polyesters”; polymers of bisphenol and dicarboxylic acids, known as “polyarylates”; and polymers of vinyl chlorides, known as “polyvinyl chlorides” (PVC).
High performance thermoplastics may exhibit extraordinary properties. For example, polyphenylene sulfide (PPS), has exceptionally high strength and rigidity, polyether ketone (PEK), polyether ether ketone (PEEK), and polyamide imide (PAI) have very high strength and rigidity, as well as exceptional heat resistance, and polyetherimide (PEI) has inherent flame resistance. Unusual thermoplastics include ionomers, in particular, copolymers of ethylene and methacrylic acid that have ionic rather than covalent crosslinking, which results in behavior resembling that of thermoset plastics in their operating range; polyvinylcarbazole, which has unique electrical properties; and polymers of isobutylene, known as “polyisobutylenes,” which are viscous at room temperature.
Thermoset plastics are synthetic resins that are typically permanently changed upon thermal curing, that is, they solidify into an infusible state so that they do not soften and become plastic again upon subsequent heating. However, certain thermoset plastics may exhibit thermoplastic behavior over a limited portion of their useful application ranges, and are similarly useful as matrix components in applications employing exemplary embodiments of the products disclosed herein. Some types of thermoset plastics, especially certain polyesters and epoxides, are capable of cold curing at room temperature. Thermoset plastics include alkyds, phenolics, epoxides, aminos (including urea-formaldehyde and melamine-formaldehyde), polyimides, and some silicon plastics.
The adhesion of the polymer matrix onto filler particles can impact the reinforcement provided by the filler. The mechanical properties can be further enhanced if the polymer matrix adheres to the filler particle surface through chemical coupling agents such as silanes.